Improved Methods for Quantifying and Designing for Impact Damage Tolerance

J.C. MEEKER, M. GRAN and J.F. SCHUTTE

Abstract

Aerospace industry primes have indicated that improvements to current methods for characterizing damage tolerance of full-scale composite structures are needed. A methodology to address this need is being developed that utilizes experimental results correlated with analysis models to enable a reduction in time and funding resources required to demonstrate that damage tolerance requirements of a composite structure have been met. The subject of the work outlined in this document was a scale-up effort, extending the scope of traditional coupon level experimental and analysis approaches to include larger representative structural elements. This effort is intended to lay the foundation for designing a modified damage tolerance test procedure that more closely replicates loads and failure modes observed in composite airframe and nacelle structures. Once validated, this combined experimental/analysis approach will significantly reduce the number of tests required for airframe designers to demonstrate damage tolerance of composite structures. This paper outlines part of the validation effort undertaken to correlate a finite element (FE) nonlinear buckling numerical simulation to a set of coupon and scaled-up blade stiffened panel test results. The explicit FE analysis approach incorporates a user defined nonlinear material subroutine (VUMAT) to capture material softening behavior due to fiber and matrix failure modes. Two numerical models were evaluated, a 4â€x6â€ test coupon, and a scaled up 10â€x12â€ double blade stiffened panel, with both subjected to in-plane compression loads.